use substrate saturating conditions with assay temperature and pH approximating field

conditions. However, temperatures as high as 45 'C have been used (Sinsabaugh et al.,

1991). Sample alkalinization prior to fluorescence measurement is also often performed

to maximize the fluorescence intensity (Freeman et al., 1995).

 Enzyme activity is generally more resolvable with substrate saturation and the

resultant generally linear function of enzyme activity allows for shorter incubation times

and less error. Strong correlations in the literature between potential enzyme activities

and nutrient conditions or correlated processes allow enzyme activities to reflect the

magnitude or process relationships among samples or between systems (Cembella et al.,

1984; Jansson et al., 1988; Foreman et al., 1998).

 The methodological heterogeneity of enzyme assays is a reflection of ecological

diversity and localized microbial community structures among studies. For example,

substrate incubation times in the literature range from 10 minutes to 3 days (Miettinen et

al., 1996; Foreman et al., 1998; Debosz et al., 1999; Burns and Ryder, 2001; Kourtev et

al., 2002b). Assay incubation times are generally based on the ability to measure within

the linear portion of the time curve while limiting the opportunity for microbial growth

(Freeman et al., 1995, 1996). Reported MUF and AMC substrate concentrations are also

highly variable between studies and ranges from 1 to 500 [tM in soil and water column

enzyme studies (Chr6st, 1989; Sinsabaugh et al., 1997; Debosz et al., 1999; Bums and

Ryder, 2001; Shackle et al., 2000; Sinsabaugh and Foreman, 2001; Saiya-Cork et al.,

2002; Wittmann et al., 2004). An emphasis of setting substrate concentrations at

saturating conditions has been documented in several studies (Chr6st, 1989; Sinsabaugh

and Findlay, 1995; Burns and Ryder, 2001).